The present application claims priority under 35 U.S.C. xc2xa7 119 of German Patent Application No. 100 08 800.7, filed on Feb. 25, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a calender roll having a roll jacket that surrounds an inner chamber. Furthermore, the invention relates to a process for operating the calender roll having a roll jacket that surrounds an inner chamber.
2. Discussion of Background Information
Such calender rolls are frequently used as center rolls in a calender, thus forming a part of a roll stack. Here, neighboring rolls form nips, through which a material web is guided in order to be exposed to an increased pressure or perhaps an increased temperature.
Such rolls are widely used for the processing of a paper web which in the following is used as the example for describing the invention. However, the same problems occur with other material webs as well.
In such calenders, usually so-called xe2x80x9csoftxe2x80x9d rolls cooperate with xe2x80x9chardxe2x80x9d rolls. Sporadically, two xe2x80x9csoftxe2x80x9d rolls cooperate. Here, the soft rolls are covered with a plastic cover. It has been observed that after a certain duration of operation a so-called bar ring can be observed. This bar ring appearance causes, on the one hand, an undesired lined pattern on the paper web. However, these lines are also discernible as lineshaped markings on the elastic rolls with the plastic covers. The soft rolls become multi-angular, so to speak. A certain depth and intensity on these bar rings leads to rejections in the paper web. Then the correlating roll or the correlating rolls must be reworked in order to remove the deformation of the plastic cover. This is generally done by turning the roll off on the lathe.
The invention is based on the aspect of avoiding the appearance of bar rings. This aspect is attained in a process of the type described at the outset such that an active oscillation is created in the inner chamber that affects the roll jacket.
A roll stack formed from several rolls has a multitude of natural frequencies. Among these natural frequencies there are, for instance, natural sagging frequencies that are of lesser interest in the present case, and forms of natural oscillations that result from the oscillating roll masses on the spring and damper systems that are formed by the plastic covers positioned between the rolls and also by the roll bearings. An operating calender creates exciting forces whose frequencies are dependent on the roll rotations and are equivalent to a multiple of the rotation frequency in the first feeding. These exciting forces can have many causes, for instance, inhomogeneities, anisotropies, or geometric faults. Also, variations in paper thickness of the paper web traveling through the calender can excite the roll stack. When one of these exciter frequencies meets one of the natural frequencies the oscillating system reacts with increased oscillation amplitudes. Due to the multitude of possible forms of natural oscillations these resonance points are practically unavoidable in the construction.
Generally, the oscillation system is dampened to such an extent and the exciter forces are so small that the resulting oscillating motion is not immediately disturbing. Over a more or less long duration, however, these oscillating motions imprint the plastic cover of the elastic roll. Frequently it can be observed that the nearest integral multiple of the oscillation frequency is imprinted onto the roll as a pattern. Thus, a feedback of the oscillation occurs. The oscillation amplitudes then rise exponentially. They are expressed, on the one hand, by an increased sound level (up to more than 115 dB (A)) and, on the other hand, in periodical thickness variations of the paper web passing through which lead to rejections, as mentioned above.
According to the invention, the feedback effect of the creating mechanism of the periodic cover waviness is disturbed in order to prevent the above-described feedback. In order to avoid that an even integral pattern with a frequency close to the natural frequency of the system is imprinted onto the rolls, an oscillation that feeds back to the roll jacket is actively created in the inner chamber of the calender roll. In addition to the oscillations at the calender that can be observed at the roll jacket during operation, the roll jacket is caused to oscillate as well. This results in a common oscillation behavior of a single roll in which, in the ideal case, the oscillations excited from the calender are eliminated by the active oscillation created in the inner chamber of the calender roll. Frequently, this can only be achieved with difficulties in practical use. Therefore, it will frequently be sufficient to control the active oscillation such that the resulting oscillation of the calender roll does not result in a bar ring formation.
Here, it is preferred that a resulting oscillation is determined at the roll jacket and the active oscillation is controlled dependent on the resulting oscillation, i.e., an active oscillation is created in a control circuit that is designed such that the resulting oscillation is as small as possible.
Preferably, the frequency and/or the phase of the active oscillation is modified during operation. It can, for instance, be provided that the frequency and/or phase of the active oscillation is modified from time to time or continuously. To express it even more generally, the spectral parts of the active oscillation can be modified during operation with regard to their amplitudes, frequencies and/or phases. This causes the surface of the plastic cover to deform so that the impression of bar rings or the multi angularity can be avoided.
Preferably, the active oscillation is directed essentially in the pressing direction of the roll. This is the direction from which the strongest influence for the formation of bar rings is to be expected according to present knowledge. When the active oscillation of the exciter oscillation counteracts here. its impact is the largest.
This aspect is attained in a calender roll of the above-mentioned type such that at least one actuator effecting the roll jacket is provided in the inner chamber. Such an actuator can impose an oscillation onto the roll jacket. This oscillation is then the above-mentioned xe2x80x9cactive oscillation.xe2x80x9d The oscillation caused by external exciters and the oscillation of the roll jacket caused by the actuator result then in a common oscillation that can be formed by a corresponding control of the actuator such that the formation of bar rings is avoided or at least reduced.
Here, it is preferred to position the actuator between an inertia mass and the roll jacket. This increases the effectiveness of the actuator. For example, the actuator can be embodied such that it enlarges or reduces the distance between the inertia mass and the roll jacket which requires a shifting of the inertia mass. In this case, due to the inertia of the inertia mass a reaction force develops at the roll jacket that can be used for the creation of an active oscillation.
Preferably, several actuators are distributed over the axial length of the roll jacket. This is due to the fact that many roll jackets are flexible to the extent that an impulse of an actuator positioned in the middle is not necessarily sufficient in order to make the correlating active oscillation reach to the edge strips of the roll. When several actuators are distributed in the axial direction it can be ensured that the calender roll is excited over its entire axial length. Such embodiments are certainly preferred in which all such actuators are operated in a synchronized manner or at least by the same means.
Preferably, at least two actuators, impacting perpendicular to the roll axis and being positioned essentially at the same axial position, are combined to a group. This results easily in the ability to influence the direction of the exciting. Each actuator creates a reaction force onto the roll jacket independently from the other ones of the same group. The combined force results then in the net force of the reaction forces.
Here, it is particularly preferred to position the actuators belonging to the same group rotationally symmetrical around the roll axis. In this case, at least two dual acting actuators or three single acting actuators are necessary. Then, essentially, any direction of oscillation can be adjusted without losing the symmetry inside of the roll.
In the roll jacket a sensor arrangement is provided, preferably, that is connected to a control device that controls at least one actuator. With the aid of the sensor arrangement the oscillations effecting the roll jacket can be measured. Since the sensor arrangement is also positioned in the inner chamber the oscillation can even be measured reliably when the roll contacts another roll during operation and particularly in the area where the oscillations to be expected are the largest, therefore no construction space for sensors is available on the outside. However, in the interior of the roll, space is available that can be used for the positioning of the sensor arrangement. This is additionally advantageous for detecting the oscillations of the roll practically at the position where also the counter oscillations are created by the actuators.
Preferably, the control device is provided with a rotation entry and/or a rotation angle entry. With it the rotation or the rotation angle of the roll can be taken into account for the creation of the active oscillations by the actuators. This improves the reacting behavior of the control device.
In a preferred embodiment the actuators are provided with electromagnets. Electromagnets are easily controlled. They can operate with relatively high frequencies of about 400 to 800 Hz and cause correlating oscillations in the roll jacket.
In a particularly preferred embodiment it is provided for the actuator to rotate together with the roll jacket. In this case, there is a permanent coupling of the actuator with the roll jacket, thus no bearing needs to be provided between the actuator and the roll jacket. By controlling the actuator or actuators accordingly even in a rotating actuator it can be ensured that the oscillation is pointed in the desired direction.
Preferably, an electrical energy transmission device is provided at the end of the roll jacket. With the aid of the energy transmission device the energy necessary for operating the actuators is transmitted from the outside into the inside of the roll. In one case, the electrical energy can directly affect the actuators. However, it is also possible to provide another electromagnetic transmission and to drive the actuators hydraulically or pneumatically, for instance, when an electric motor for driving a pump is positioned inside of the roll. For the sake of simplicity, however, the following is conditioned in the actuators being driven electrically.
Here, it is preferred that the electric energy transmission device is provided with a slip ring arrangement. A slip ring arrangement forms slipping contacts over which the electric current can be guided into the interior of the roll using a certain voltage. This is a very simple and proven embodiment.
In an alternative embodiment the electric energy transmission device can be provided with an inductive coupling. Thus, this is a transformer with a stationary part and a part rotating together with the roll. Through such an inductive transmission electric energy can also be brought into the interior of the roll. Here, it must be considered that the energy required for the actuators is not very high. It is in the range of Kilowatts so that relatively compact slip ring arrangements or transformer arrangements are sufficient to transmit sufficient electric power.
Preferably, a modulation device is provided between the energy transmission device and an energy providing device that feeds a signal into the transmitted electric energy. Here, modulation is regarded in the sense of providing the current or the voltage that is transmitted into the interior of the roll with information that can be used for controlling the actuators. This modulation can occur in many ways. For example, a multiplexer can be used that transmits signals and power in subsequent periods. It is also possible to xe2x80x9caddxe2x80x9d a correspondingly higher frequenced signal of the type of carrier frequency modulation onto the electric power when it is transmitted with the aid of direct current or with the aid of a low-frequency alternating current.
In an alternative embodiment it can be provided that a generator is provided in the roll jacket that is driven by the rotation of the roll. This generator can be an electric generator or an electric or pneumatic pump. In this case, however, a slightly higher driving power is necessary for the roll. The energy necessary for driving the actuators can also be received without any additional energy transmission device from the outside towards the inside.
Preferably, the roll jacket is provided in the area of each actuator with a cage-like support structure. Here, the actuator does not need to impact the roll jacket immediately, perhaps being faced by a warped or concave area. It can act onto the support structure which then transmits the reaction forces onto the roll jacket.
According to an aspect of the present invention, a process for operating a calender roll including a roll jacket surrounding an inner chamber is provided. The process includes creating an active oscillation in the inner chamber that acts upon the roll jacket. According to another aspect of the present invention, the process further includes determining a resulting oscillation at the roll jacket; and controlling the active oscillation depending on the resulting oscillation.
Additionally, other aspects of the present invention include modifying the active oscillation is during operation with regard to at least one of amplitude, frequency, and phase. In yet another aspect of the present invention, at least one of the frequency and the phase of the active oscillation varies during operation. In another aspect of the present invention, the active oscillation is modified during operation. In another aspect of the present invention, the active oscillation is modified continuously during operation. According to a further aspect of the present invention, the active oscillation is directed in the press direction of the roll.
In another aspect of the present invention, a calender is provided including a roll jacket surrounding an inner chamber, and at least one actuator provided within the inner chamber acting upon the roll jacket. According to a further aspect of the present invention, the actuator is positioned between an inertia mass and an inside surface of the roll jacket. In another aspect of the invention, the said at least one actuator includes a plurality of actuators distributed substantially over an entire axial length of the roll jacket.
According to a still further aspect of the present invention, at least two actuators which act perpendicular to an axis of the calender roll, are positioned at a same axial position and are grouped together. Other aspects of the invention, include positioning the at least two actuators radially symmetrically around the axis of the calender roll.
Further aspects of the present invention include a sensor arrangement provided inside the roll jacket that is connected to a control device that controls at least one actuator. According to still other aspects of the present invention, the control device is provided with at least one of a rotation entry and a rotation angle entry. According to another aspect of the present invention, the at least one actuator is provided with at least one electromagnet.
According to still another aspect of the invention, the said at least one actuator rotates together with the roll jacket. According to another aspect of the present invention, an electric energy transmission device provided at an end of the roll jacket. Additionally, other aspects of the present invention include the electric energy transmission device is provided with a slip ring arrangement. In yet another aspect of the present invention, a performance enhancer which controls the at least one actuator is provided.
In another aspect of the present invention, the electric energy transmission device is provided with an inductive coupling. According to a further aspect of the present invention, a modulation device is provided, connected between the energy transmission device and an energy supply device, that inserts a signal into electric energy from the energy supply device.
According to another aspect of the present invention, the modulation device includes a multiplexer and de-multiplexer. Additionally, other aspects of the present invention include a generator that is provided within the roll jacket that is driven by rotation of the calender roll. In yet another aspect of the present invention, a cage structure provided within the inner chamber of the roll jacket to provide support in the area of the at least one actuator is included.
In another aspect of the present invention, the cage structure include four plates forming a centric positioned square supported at an inner wall of the roll jacket. According to a still further aspect of the present invention, at the center of the centric positioned square, an inertia mass is provided onto which four actuators are provided. According to a still further aspect of the present invention, the four actuators include electromagnets.
In another aspect of the present invention, each electromagnet includes an E-shaped yoke, having a plurality of arms, with a reel being positioned around a center arm of the E-shaped yoke. According to a still further aspect of the present invention, the plurality of arms of the yoke, together with the cage arrangement, form a gap. Other aspects of the present invention include a speedometer. Further aspects of the present invention include a signal processor to gather information with respect to the rotational angle of the calender roll.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.